The present invention relates to novel antagonists of endothelin useful as pharmaceutical agents, to methods for their production, to pharmaceutical compositions which include these compounds and a pharmaceutically acceptable carrier, and to pharmaceutical methods of treatment. More particularly, the novel compounds of the present invention are antagonists of endothelin useful in treating elevated levels of endothelin, acute and chronic renal failure, hypertension, myocardial infarction, metabolic, endocrinological and neurological disorders especially cerebral vasospasm, stroke, and head injury, congestive heart failure, endotoxic shock, subarachnoid hemorrhage, arrhythmias, asthma, preeclampsia, atherosclerotic disorders including Raynaud's disease, restenosis, angina, cancer, pulmonary hypertension, ischemic disease, gastric mucosal damage, hemorrhagic shock, ischemic bowel disease, and diabetes.
Endothelin-1 (ET-1), a potent vasoconstrictor, is a 21 amino acid bicyclic peptide that was first isolated from cultured porcine aortic endothelial cells. Endothelin-1, is one of a family of structurally similar bicyclic peptides which include; ET-2, ET-3, vasoactive intestinal contractor (VIC), and the sarafotoxins (SRTXs). The unique bicyclic structure and corresponding arrangement of the disulfide bridges of ET-1, which are the same for the endothelins, VIC, and the sarafotoxins, has led to significant speculation as to the importance of the resulting induced secondary structure to receptor binding and functional activity. ET-1 analogues with incorrect disulfide pairings exhibit at least 100-fold less vasoconstrictor activity. The flexible C-terminal hexapeptide of ET-1 has been shown to be important for binding to the ET receptor and functional activity in selected tissues. Additionally, the C-terminal amino acid (Trp-21) has a critical role in binding and vasoconstrictor activity, since ET[1-20] exhibits approximately 1000-fold less functional activity.
Endothelin is involved in many human disease states.
Several in vivo studies with ET antibodies have been reported in disease models. Left coronary artery ligation and reperfusion to induce myocardial infarction in the rat heart, caused a four- to seven-fold increase in endogenous endothelin levels. Administration of ET antibody was reported to reduce the size of the infarction in a dose-dependent manner (Watanabe T., et al., "Endothelin in Myocardial Infarction," Nature (Lond.), 344:114 (1990)). Thus, ET may be involved in the pathogenesis of congestive heart failure and myocardial ischemia (Margulies K. B., et al., "Increased Endothelin in Experimental Heart Failure," Circulation, 82:2226 (1990)).
Studies by Kon and colleagues using anti-ET antibodies in an ischemic kidney model, to deactivate endogenous ET, indicated the peptide's involvement in acute renal ischemic injury (Kon V., et al., "Glomerular Actions of Endothelin In Vivo," J. Clin. Invest., 83:1762 (1989)). In isolated kidneys, preexposed to specific antiendothelin antibody and then challenged with cyclosporine, the renal perfusate flow and glomerular filtration rate increased, while renal resistance decreased as compared with isolated kidneys preexposed to a nonimmunized rabbit serum. The effectiveness and specificity of the anti-ET antibody were confirmed by its capacity to prevent renal deterioration caused by a single bolus dose (150 pmol) of synthetic ET, but not by infusion of angiotensin II, norepinephrine, or the thromboxane A.sub.2 mimetic U-46619 in isolated kidneys (Perico N., et al., "Endothelin Mediates the Renal Vasoconstriction Induced by Cyclosporine in the Rat," J. Am. Soc. Nephrol,, 1:76 (1990)).
Others have reported inhibition of ET-1 or ET-2-induced vasoconstriction in rat isolated thoracic aorta using a monoclonal antibody to ET-1 (Koshi T., et al., "Inhibition of Endothelin (ET)-1 and ET-2-Induced Vasoconstriction by Anti-ET-1 Monoclonal Antibody," Chem. Pharm. Bull., 39:1295 (1991)).
Combined administration of ET-1 and ET-1 antibody to rabbits showed significant inhibition of the blood pressure (BP) and renal blood flow responses (Miyamori I., et al., "Systemic and Regional Effects of Endothelin in Rabbits: Effects of Endothelin Antibody," Clin. Exp. Pharmacol. Physiol., 17:691 (1990)).
Other investigators have reported that infusion of ET-specific antibodies into spontaneously hypertensive rats (SHR) decreased mean arterial pressure (MAP), and increased glomerular filtration rate and renal blood flow. In the control study with normotensive Wistar-Kyoto rats (WKY) there were no significant changes in these parameters (Ohno A., "Effects of Endothelin-Specific Antibodies and Endothelin in Spontaneously Hypertensive Rats," J. Tokyo Women's Med. Coll., 61:951 (1991)).
In addition, elevated levels of endothelin have been reported in several disease states (see Table I below).
Burnett and co-workers recently demonstrated that exogenous infusion of ET (2.5 ng/kg/mL) to anesthetized dogs, producing a doubling of the circulating concentration, did have biological actions (Lerman A., et al., "Endothelin has Biological Actions at Pathophysiological Concentrations," Circulation, 83:1808 (1991)). Thus heart rate and cardiac output decreased in association with increased renal and systemic vascular resistances and antinatriuresis. These studies support a role for endothelin in the regulation of cardiovascular, renal, and endocrine function.
In the anesthetized dog with congestive heart failure, a significant two- to three-fold elevation of circulating ET levels has been reported (Cavero P. G., et al., "Endothelin in Experimental Congestive Heart Failure in the Anesthetized Dog," Am. J. Physiol., 259:F312 (1990)), and studies in humans have shown similar increases (Rodeheffer R. J., et al., "Circulating Plasma Endothelin Correlates With the Severity of Congestive Heart Failure in Humans," Am. J. Hypertension, 4:9A (1991)). When ET was chronically infused into male rats, to determine whether a long-term increase in circulating ET levels would cause a sustained elevation in mean arterial blood pressure, significant, sustained, and dose-dependent increases in mean arterial BP were observed. Similar results were observed with ET-3 although larger doses were required (Mortenson L. H., et al., "Chronic Hypertension Produced by Infusion of Endothelin in Rats," Hypertension, 15:729 (1990)).
The distribution of the two cloned receptor subtypes, termed ET.sub.A and ET.sub.B, have been studied extensively (Arai H., et al., Nature, 348:730 (1990), Sakurai T., et al., Nature, 348:732 (1990)). The ET.sub.A, or vascular smooth muscle receptor, is widely distributed in cardiovascular tissues and in certain regions of the brain (Lin H. Y., et al., Proc. Natl. Acad. Sci., 88:3185 (1991)). The ET.sub.B receptor, originally cloned from rat lung, has been found in rat cerebellum and in endothelial cells, although it is not known if the ET.sub.B receptors are the same from these sources. The human ET receptor subtypes have been cloned and expressed (Sakamoto A., et al., Biochem. Biophys. Res. Chem., 178:656 (1991), Hosoda K., et al., FEBS Lett., 287:23 (1991)). The ET.sub.A receptor clearly mediates vasoconstriction and there have been a few reports implicating the ET.sub.B receptor in the initial vasodilatory response to ET (Takayanagi R., et al., FEBS Lett., 282:103 (1991)). However, recent data has shown that the ET.sub.B receptor can also mediate vasoconstriction in some tissue beds (Panek R. L., et al., Biochem. Biophys. Res. Commun., 183(2):566 (1992)).
Comparison of the receptor affinities of the ETs and SRTXs in rats and atria (ET.sub.A) or cerebellum and hippocampus (ET.sub.B), indicate that SRTX-c is a selective ET.sub.B ligand (Williams D. L., et al., Biochem. Biophys. Res. Commun., 175:556 (1991)). A recent study showed that selective ET.sub.B agonists caused only vasodilation in the rat aortic ring, possibly through the release of EDRF from the endothelium (ibid). Thus, reported selective ET.sub.B agonists, for example, the linear analog ET[1,3,11,15-Ala] and truncated analogs ET[6-21, 1,3,11,15-Ala], ET[8-21,11,15-Ala], and N-Acetyl-ET[10-21,11,15-Ala] caused vasorelaxation in isolated, endothelium-intact porcine pulmonary arteries (Saeki T., et al., Biochem. Biophys. Res. Commun., 179:286 (1991)). However, some ET analogs are potent vasoconstrictors in the rabbit pulmonary artery, a tissue that appears to possess an ET.sub.B y, nonselective type of receptor (ibid).
Plasma endothelin-1 levels were dramatically increased in a patient with malignant hemangioendothelioma (Nakagawa K., et al., Nippon Hifuka Gakkai Zasshi, 100:1453-1456 (1990)).
The ET receptor antagonist BQ-123 has been shown to block ET-1 induced bronchoconstriction and tracheal smooth muscle contraction in allergic sheep providing evidence for expected efficacy in bronchopulmonary diseases such as asthma (Noguchi, et al., Am. Rev. Respir. Dis. 415(4 Part 2):A858 (1992)).
Circulating endothelin levels are elevated in women with preeclampsia and correlate closely with serum uric acid levels and measures of renal dysfunction. These observations indicate a role for ET in renal constriction in preeclampsia (Clark B. A., et al., Am. J. Obstet, Gynecol., 166:962-968 (1992)).
Plasma immunoreactive endothelin-1 concentrations are elevated in patients with sepsis and correlate with the degree of illness and depression of cardiac output (Pittett J., et al., Ann Surg., 213(3):262 (1991)).
In addition the ET-1 antagonist BQ-123 has been evaluated in a mouse model of endotoxic shock. This ET.sub.A antagonist significantly increased the survival rate in this model (Toshiaki M., et al., 20.12.90. EP 0 436 189 A1).
Endothelin is a potent agonist in the liver eliciting both sustained vasoconstriction of the hepatic vasculature and a significant increase in hepatic glucose output (Gandhi C. B., et al., Journal of Biological Chemistry, 265(29):17432 (1990)). In streptozotocin-diabetic rats there is an increased sensitivity to endothelin-1 (Tammesild P. J., et al., Clin. Exp. Pharmacol. Physiol., 19(4):261 (1992)). In addition increased levels of plasma ET-1 have been observed in microalbuminuric insulin-dependent diabetes mellitus patients indicating a role for ET in endocrine disorders such as diabetes (Collier A., et al., Diabetes Care, 15(8):1038 (1992)).
ET.sub.A antagonist receptor blockade has been found to produce an antihypertensive effect in normal to low renin models of hypertension with a time course similar to the inhibition of ET-1 pressor responses (Basil M. K., et al., J. Hypertension, 10(Suppl. 4):S49 (1992)). The endothelins have been shown to be arrhythmogenic, and to have positive chronotropic and inotropic effects, thus ET receptor blockade would be expected to be useful in arrhythmia and other cardiovascular disorders (Hah S.-P., et al., Life Sci., 46:767 (1990)).
The widespread localization of the endothelins and their receptors in the central nervous system and cerebrovascular circulation has been described (Nikolov R. K., et al., Drugs of Today, 28(5):303-310 (1992)). Intracerebroventricular administration of ET-1 in rats has been shown to evoke several behavioral effects. These factors strongly suggest a role for the ETs in neurological disorders. The potent vasoconstrictor action of ETs on isolated cerebral arterioles suggests the importance of these peptides in the regulation of cerebrovascular tone. Increased ET levels have been reported in some CNS disorders, i.e., in the CSF of patients with subarachnoid hemorrhage and in the plasma of women with preeclampsia. Stimulation with ET-3 under conditions of hypoglycemia have been shown to accelerate the development of striatal damage as a result of an influx of extracellular calcium. Circulating or locally produced ET has been suggested to contribute to regulation of brain fluid balance through effects on the choroid plexus and CSF production. ET-1 induced lesion development in a new model of local ischemia in the brain has been described.
Circulating and tissue endothelin immunoreactivity is increased more than twofold in patients with advanced atherosclerosis (Lerman A., et al., New England J. Med., 325:997-1001 (1991)). Increased endothelin immunoreactivity has also been associated with Buerger's disease (Kanno K., et al., J. Amer. Med. Assoc., 264:2868 (1990)) and Raynaud's phenomenon (Zamora M. R., et al., Lancet, 336:1144-1147 (1990)). Likewise, increased endothelin concentrations were observed in hypercholesterolemic rats (Horio T., et al., Atherosclerosis, 89:239-245 (1991)).
An increase of circulating endothelin levels was observed in patients that underwent percutaneous transluminal coronary angioplasty (PTCA) (Tahara A., et al., Metab. Clin. Exp., 40:1235-1237 (1991) , Sanjay K., et al., Circulation, 84(Suppl. 4):726 (1991)).
Increased plasma levels of endothelin have been measured in rats (Stelzner T. J., et al., Am. J. Physiol., 262:L614-L620 (1992)) and individuals (Miyauchi T., et al., Jpn. J. Pharmacol., 58:279P (1992) and Stewart D. J., et al., Ann. Internal Medicine, 114:464-469 (1991)) with pulmonary hypertension.
Elevated levels of endothelin have also been measured in patients suffering from ischemic heart disease (Yasuda M., et al., Amer. Heart J., 119:801-806 (1990), Ray S. G., et al., Br. Heart J., 67:383-386 (1992)) and either stable or unstable angina (Stewart J. T., et al., Br. Heart J., 66.:7-9 (1991)).
Infusion of an endothelin antibody 1 hour prior to and 1 hour after a 60 minute period of renal ischaemia resulted in changes in renal function versus control. In addition, an increase in glomerular platelet-activating factor was attributed to endothelin (Lopez-Farre A., et al., J. Physiology, 444:513-522 (1991)). In patients with chronic renal failure as well as in patients on regular hemodialysis treatment, mean plasma endothelin levels were significantly increased (Stockenhuber F., et al., Clin. Sci. (Lond.), 82:255-258 (1992)). In addition, it has been suggested that the proliferative effect of endothelin on mesangial cells may be a contributing factor in chronic renal failure (Schultz P. J., J. Lab. Clin. Med., 119:448-449 (1992,).
Local intra-arterial administration of endothelin has been shown to induce small intestinal mucosal damage in rats in a dose-dependent manner (Mirua S., et al., Digestion, 48:163-172 (1991)). Administration of endothelin-1 in the range of 50-500 pmol/kg into the left gastric artery increased the tissue type plasminogen activator release and platelet activating formation, and induced gastric mucosal hemorrhagic change in a dose dependent manner (Kurose I., et al., Gut, 33:868-871 (1992)). Furthermore, it has been shown that an anti-ET-1 antibody reduced ethanol-induced vasoconstriction in a concentration-dependent manner (Masuda E., et al., Am. J. Physiol., 262:G785-G790 (1992)). Elevated endothelin levels have been observed in patients suffering from Crohn's disease and ulcerative colitis (Murch S. H., et al., Lancet, 339:381-384 (1992)).
The role of endothelins (ET-1, -2, -3) in various physiological and pathophysiological conditions has been studied extensively (Doherty A. D., Endothelin: A New Challenge, J. Med. Chem,, 35:1493 (1992); Simonson M. S., Endothelins: Multifunctional Renal Peptides, Physiological Reviews 79:375 (1993)). These peptides act via their receptors viz. ET.sub.A and ET.sub.B, which have been cloned and expressed. ET.sub.A specific antagonists have been identified viz. BQ123 (Ishikawa K.; Fukami T., et al., Cyclic pentapeptide endothelin antagonists with high ET.sub.A selectivity, Potency- and solubility-enhancing modifications, J. Med. Chem., 35:2139 (1992); Kiyofumi I., et al., Endothelin antagonistic cyclic pentapeptides. EPA 0436 189 A1 published Jul. 10, 1991), BMS182874 (Stein P. D., et al., Sulfonamide endothelin antagonists. EP 0558258 A1, published Sep. 1, 1993) and FR 139317 (Keiji H., et al., Peptides having endothelin antagonist activity, a process for the preparation thereof and pharmaceutical compositions comprising the same. EP 0457195 A2, published Nov. 21, 1991). Several non-selective ET.sub.A /ET.sub.B antagonists have also been identified including PD 142893 (Cody W. L., et al., Design of a functional hexapeptide antagonist of endothelin, J. Med. Chem., 35:3301 (1992); Doherty A. M., et al., Structure-activity relationships of C-terminal endothelin hexapeptide antagonists, J. Med. Chem., 36:2585 (1993)), PD 145065 (Cody W. L., et al., The rational design of a highly potent combined ET.sub.A and ET.sub.B receptor antagonist (PD 145065) and related analogues, Med. Chem. Res., 3:154 (1993); Doherty A. M., et al., In vitro and in vivo studies with a series of hexapeptide endothelin antagonists, J. Cardiovasc. Pharmacol. 1993, in press), Ro 46-2005 (Burri K., et al., Application of sulfonamides as therapeutics and new sulfonamides. EP 0510526 A1, published Oct. 28, 1992; Clozel M., et al., The discovery of Ro 46-2005, an orally available non-peptide antagonist of ET.sub.A and ET.sub.B receptors. 3rd International Endothelin Symposium, Houston, Tex., February 1993; Clozel M., et al., Pathophysiological role of endothelin revealed by the first orally active endothelin receptor antagonist, Nature, 365:759 (1993)), and Ro 47-0203 (Roux S. P., et al., Ro 47-0203, a new endothelin receptor antagonist reverses chronic vasospasm in experimental subarachnoid hemorrhage, Circulation, 4(Part 2, Supplement):I-170 (1993)). These antagonists have blocked the vasoconstrictive effects of ET peptides in several in vivo disease models.
For example, BQ123 has been effective in antagonizing the ET-1 induced pressor response in conscious rats (Ihara M., et al., In vitro biological profile of highly potent novel endothelin (ET) antagonist BQ-123 selective for the ET.sub.A receptor, J. Cardiovasc. Pharmacol., 20(S12):S11 (1992); Ihara M., et al., Biological profiles of highly potent novel endothelin antagonists selective for the ET.sub.A receptor, Life Sci., 50:247 (1992)). Intravenous infusion of BQ123 decreased blood pressure significantly in stroke prone spontaneous hypertensive rats and was effective in the prevention of acute hypoxia induced pulmonary hypertension (McMahon E. G., et al., Effect of phosphoramidon (endothelin converting enzyme inhibitor) and BQ-123 (Endothelin receptor subtype-A antagonist) on blood pressure in hypertensive rats, Am. J. Hypertension, 6:667 (1993)). ET-1 induced vasoconstriction in rabbit retinal arteries and the renal vascular resistance in rats was blocked by i.v. BQ123 (Takei K., et al., Analysis of vasocontractile response to endothelin-1 in rabbit retinal vessels using an ET.sub.A receptor antagonist and an ET.sub.B receptor agonist, Life Sci., 53:PL111 (1993)). Cyclosporine A (CsA) induced ET-1 release in vivo (Fogo A., et al., Severe endothelial injury in a renal transplant patient receiving cyclosporine, Transplantation, 49:1190 (1990); Watschinger B., et al., Cyclosporine A toxicity is associated with reduced endothelin immunoreactivity in renal endothelium, Transplant. Proc., 24:2618 (1992); Awazu M., et al., Cyclosporine promotes glomerular endothelin binding in vivo, J. Am. Soc. Nephrol., 1:1253 (1991); Bloom I. T., et al., Acute cyclosporine-induced renal vasoconstriction is mediated by endothelin-1, Surgery, 114:480 (1993)), which caused renal vasoconstriction (Kon V. and Awazu M., Endothelin and cyclosporine nephrotoxicity, Renal Fall., 14:345 (1992); Brooks D. P., et al., Effect of nifedipine on cyclosporine A-induced nephrotoxicity, urinary endothelin excretion and renal endothelin receptor number, Eur. J. Pharmacol., 194:115 (1991,). This acute CsA toxicity was suppressed by BQ123 in a rat model (Fogo A., et al., Endothelin receptor antagonism is protective in in vivo acute cyclosporin toxicity, Kidney Int., 42:770 (1992)). BQ123 (i.v.) prevents the mitochondrial [Ca.sup.2+ ] accumulation in the early phase of ischemic acute renal failure in rats and protects proximal tubular cells from post-ischemic degeneration suggesting possible involvement of endothelin in the pathogenesis of tubular cell injury in the acute ischemic renal failure model (Mino N., et al., Protective effect of a selective endothelin receptor antagonist, BQ-123, in ischemic acute renal failure in rats, Eur. J. Pharmacol., 221:77 (1992)).
Intraperitoneal administration of FR 139317 in rats reduced abnormal permeability to proteins and limited glomerular injury and prevented renal function deterioration. Intracisternal administration of FR 139317 significantly reduced the vasoconstriction of the basilar artery in canine subarachnoid hemorrhage model (Nirei H., et al., An endothelin ET.sub.A receptor antagonist FR 139317 ameliorates cerebral vasospasm in dogs, Life Sci., 52:1869 (1993)). ET-1 induced arrhythmia in rats (Sogabe K., et al., Pharmacological profile of FR 139317, a novel, potent endothelin ET.sub.A receptor antagonist, J. Pharmacol. Exp. Ther., 264:1040 (1993)) was also suppressed by FR 139317.
Non-selective ET.sub.A /ET.sub.B antagonists like PD 145065 and PD 142893 antagonized both pressor and depressor responses induced by ET-1 in a dose-dependent manner in anesthetized ganglionic blocked rats (Doherty A. M., et al., In vitro and in vivo studies with a series of hexapeptide endothelin antagonists, J. Cardiovasc. Pharmacol., 1993, in press). ET-1 induced reductions in renal flow in anesthetized rats (Wellings R. P., et al., Vasoconstriction in the rat kidney induced by endothelin-1 is blocked by PD 145065, Third International Conference on Endothelin, Houston, Feb. 15-17, 1993, Abstract 139) was completely inhibited by prior administration of PD 145065. In anesthetized guinea pig PD 145065 blocked the increase in pulmonary insufflation pressure induced by ET-1 (Warner T. D., et al., Inhibition by a non-selective endothelin receptor antagonist of bronchoconstrictions induced by endothelin-1 or sarafotoxin 6c in the anesthetized guinea pig, Br. J. Pharmacol. in press). Ro 46-2005 demonstrated a protective effect for renal vasoconstriction after renal ischemia in anesthetized rats and also dramatically reduced cerebral vasoconstriction after subarachnoid hemorrhage in rats. Orally administered Ro 46-2005 showed marked antihypertensive effect with a reasonably long duration (Clozel M., et al., The discovery of Ro 46-2005, an orally available non-peptide antagonist of ET.sub.A and ET.sub.B receptors, Third International Endothelin Symposium, Houston, Tex., February 1993; Clozel M., et al., Pathophysiological role of endothelin revealed by the first orally active endothelin receptor antagonist, Nature, 365:759 (1993)). Ro 47-0203 was effective in a rabbit subarachnoid hemorrhage model in reversing vasoconstriction indicating that this compound crosses the blood brain barrier (Roux S. P., et al., Ro 47-0203, a new endothelin receptor antagonist reverses chronic vasospasm in experimental subarachnoid hemorrhage, Circulation, 4(Part 2, supplement):I-170 (1993)). Ro 47-203 is reported to be in early clinical trials for SAH and hypertension (Roux S. P., et al., Ro 47-0203, a new endothelin receptor antagonist reverses chronic vasospasm in experimental subarachnoid hemorrhage, Circulation, 4(Part 2, Supplement):I-170 (1993)).
TABLE I ______________________________________ Plasma Concentrations of ET-1 in Humans RT Plasma Normal Levels Report Condition Control (pg/ml) ______________________________________ Atherosclerosis 1.4 3.2 pmol/L Surgical operation 1.5 7.3 Buerger's disease 1.6 4.8 Takayaou's arteritis 1.6 5.3 Cardiogenic shock 0.3 3.7 Congestive heart failure 9.7 20.4 (CHF) Mild CHF 7.1 11.1 Severe CHP 7.1 13.8 Dilated cardiomyopathy 1.6 7.1 Preeclampsia 10.4 pmol/L 22.6 pmol/L Pulmonary hypertension 1.45 3.5 Acute myocardial infarction 1.5 3.3 (several reports) 6.0 11.0 0.76 4.95 0.50 3.8 Subarachnoid hemorrhage 0.4 2.2 Crohn's Disease 0-24 fmol/mg 4-64 fmol/mg Ulcerative colitis 0-24 fmol/mg 20-50 fmol/mg Cold premoor test 1.2 8.4 Raynaud's phenomenon 1.7 5.3 Raynaud's/hand cooling 2.8 5.0 Hemodialysis &lt;7 10.9 (several reports) 1.88 4.59 Chronic renal failure 1.88 10.1 Acute renal failure 1.5 10.4 Uremia before hemodialysis 0.96 1.49 Uremia after hemodialysis 0.96 2.19 Essential hypertension 18.5 33.9 Sepois syndrome 6.1 19.9 Postoperative cardiac 6.1 11.9 Inflammatory arthritides 1.5 4.2 Malignant 4.3 16.2 hemangioendothelioma (after removal) ______________________________________
Rovero P., et al., British Journal of Pharmacology, 101:232-236 (1990) disclosed various analogs of the C-terminal hexapeptide of ET-1, none of which were reported to be antagonists of ET-1.
Doherty A. M., et al., Abstract, Second International Conference on Endothelin, Tsukuba, Japan, Dec. 9, 1990, and the published manuscript (J. Cardiovasc. Pharm., 17(Suppl. 7):559-561 (1991), disclosed various analogs of the C-terminal hexapeptide of ET-1, none of which exhibited any functional activity.
Copending U.S. patent application Ser. No. 07/995,480 now U.S. Pat. No. 5,382,569 discloses a series of novel antagonists of endothelin.
However, we have surprisingly and unexpectedly found that a series of C-terminal hexapeptide and related analogs of ET-1 are receptor antagonists of endothelin. Additional data for the activity of this series of peptides is found in the following references (Cody W. L., et al., J. Med. Chem., 35:3301-3303 (1992), LaDouceur D. M., et al., FASEB (1992)).